Process of steel treatment



D. l. SIMPSON.

PROCESS UF STEEL TREATMENT.

APPLICAHON HLED APH. 5, |915. RENEwiD 050.29.19ls. 1,35 1 ,494. Patented Aug. 31, 1920.

nvm/Lto@ www i l $1 l UNITED STATES PATENT OFFICE.

DAVID J. SIMPSON, 0F CHICGO, ILLINOIS, ASSIGNOR T0 NOAH STEINER AMSTUTZ, 0F VALPARAISO, INDIANA.

i A PROCESS 0F STEEL TREATMENT.

Application nled April 5, 1915, Serial No. 19,310.

To all whom 'it may concern.'

Be it known that I Davn) J. SIMPSON, citizen of the United btates, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Processes of Steel Treatment, of which the following is a specification.

lMy invention relates to improvements 1n the` process of steel treatment and it consists more especially of the steps pointed out 1n the annexed claims.

The purpose of my invention is to provide a method of steel treatment that will uniformly secure a more homogeneous characteristic of steel products than has hitherto been attainable; to secure such a relation between the particles of which the steel is composed as to insure a high elastic limit and tensile strength, with large reduction of area, and great elongation efore fracture; that will at the same time have a high degree of hardness without sacrificing toughness; that may be carried into practice without complicated and expensive devices; that is simple in the sequence of its steps; positive in results; inexpensive to operate; and economically produces products of the highest quality.

With this process a uniformity of product is secured throughout a continuous output that has not been reached heretofore. In practice a large outputl of locomotive axles covering many months was found to meet the most exacting physical tests of the purchasers without coming short on ya single specification, Whereas the lack of uniformity in quantity output when quenching, etc., is resorted to is in marked contrast to the exceptional results attained b this process.

With these and other en s in view I illustrate in the accompanying drawings such instances of `adaptation as will disclose the broad features without specifically limiting myself.

Figure 1- shows a diagrammatic relation of various means, among others, that may be used in carrying out sucl a process.

Fig. 2- shows a controlled air chamber.

Fig. 3- shows a top plan view of an arrangement of dampers.

Flg. 4- shows a side elevation of Fig. 3.

In carrying my process into practice the billets are heated in any well known manner preparatory to being hammered into the de- Specication of Letters Patent.

Patented Aug. 31, 1920.

Renewed December 29, 1919. Serial No. 348,049.

sired shape. After this the-axles are placed onto any suitable form of supports shown at 1 of Flg. 1 where they are allowed to cool to atmosp eric temperature. From here they are usually rolled by hand into the left end of furnace A onto bars of any desired cross sectlon, not shown, in order to allow' a free circulation of the heat around the axles. This provision is an obvious one and is found 1n common practice. In this furnace the axles are first heated very graduallv up to the low critical point which varies throughout a range of about 150 degrees F. between 1390 and 1240 inversely to a change 1n carbon content. From about .30 to .35% for the lowest percentage of carbon the higher temperature is required and for the higher carbons .60 to .65% a lower temperature from 1240 to 1270 suffices. An intermediate relation is 1310 to 1340o F. for .45 to .50% carbon. Other percentages of carbon bear an inverse relation to the temperature change which throughout the whole range is found to practically follow a straight line curve. During this slow rise of heat the molecular relation is readj usted so as to form a new structure. After the required temperature has been reached for a given carbon composition it is held uniform for a period of about one-third to one-half hour so as to avoid a too sudden rearrangement of the particles. This rest period is vital to the success of the process and must be carefully watched, otherwise only unsatisfactory results will be secured.

The time required to reach these temperatures varies approximately with the sizes of axles to be treated, ranging from about three hours for five inch diameters to six hours for eleven to twelve inch diameters. Cold steel should not be subjected to the extreme curve. To reach these temperatures for [ive 11( oint which ranges from 1420 to 1440 inch sections requires about one hour and or the larger diameters approximateiy three hours. By the time the second heating is completed the buggy 5 can be moved near the furnace A between it and the treatment chamber I3 ready to enter the furnace.

The axles are placed side by side in the furnace with suliicient space between them to allow the heat` to circulate. It is wide enough to form a vacant space adjacent each end of the axles into which two removable rails shown in dotted lines of Fig. 1 are quickly placed by a hoist as soon as the furnac-e doors are opened. These raiis connect with the buggy tracks at the other end of the furnace and they serve to support the buggyT as it is rapidly moved into the furnace with its main structure straddling"7 the axles. The heated axles are raised by the buggy and taken to the treatment chamber where they are lowered onto isolated supports and the buggy is removed empty from the far end of the1 chamber traversing the transfer tracks which are placed along each side of the chamber.

A hood is lowered over the deposited axles so that its edges drop into a water seal at the bottom of the chamber. The rapid cooling is effected by tiret admitting air under pressure or dry steam at about 3.5() degrees F. into the top of the hood and withdrawing it through separately controlled exit chambers to a common outlet. lVhen the treatment is completed the hood is raised and the buggy is again moved into position to lift the axles and transport them to any storage space bevond the chamber. i If after the first heat is completed there should be a doubt as to the ultimate quality the axles can be cooled to about 600 degrees F. and returned to the furnace for a draw back treatment which for .30% carbons is about 900 degrees FJ: for .50% carbon 1150 degrees F. and for .65% carbon 1260 degrees F.. other carbon contents being proportional. These draw back temperatures are to be held from one to two hours.

The furnace A may be charged by hand or otherwise from the stock rack 1. Its heat distribution may be controlled by dam-- pers whose hand levers 2 are accessible outside of the wall. Doors 3 and 4 are raised and lowered in any suitable manner. They have inspection windows and pyrometer openings. Then the heating has progressed sutiiciently the doors are opened and buggy 5 is rapidly moved into it so as to leave motor 6 on the outside. Suitable side bars with toe flanges engage the material being treated, in this instance axles, and simultaneously lift all the axles from the floor bars and in the briefest possible time transfer the lGad on track 7 to the cooling device B.

The cooling device may comprise a water verse rock shafts 13 which carry arms l that engage the dempers and as the shafts 13 are rocked by hand levers 15 the dampers are opened more or less. lt is desirable that they open more rapidly at the center than at the ends of the air chamber 1U.

A hood 16 suitably counterweighted drops into tank 8, making` an air tight chamber because of the water seal. Air is brought through pipe 17 from a suitable source passing perforated plate 18 into the open space occupied by the steel being treated. Suitable windows and pyrometer openings are provided in the sides of the hood. The hood is raised as shown in dotted lines so as to permit the buggy 5 to pass throughunder without interference.

Nhen any of the materials require a drawback they may be removed from B by hand or otherwise to the space between it and the furnace A and transferred by travelingr crane 19 to the other end of the furnace passing over it and temporarily stored on racks 1 so that the batch being heated in the furnace may be removed by the buggy without interfering with such parts that require re-heating.

It is desirable that axles 20 be suitably spaced on supporting rails 9 of the treatment chamber B in any desired manner, whether placed by hand or mechanism, so as to always lie in the proper position with res ect to the air chambers 10.

he heat of the furnace A is very intense and it is ordinarily found difficult to retain permanent metal tracks therein for a transfer buggy to travel on. One way, among many others, to overcome this difficulty is to provide removable rails that may be shoved onto the furnace door, by means of a hoist 22 operating on a track 21, before the transfer buggy reaches the furnace. These specific details of structure, etc., are embodied in a separate application bearing serial #19,312 filed April 5, 1915.

While in the furnace the materials may rest on suitable bars to permit underneath circulation. They are subjected to a suitable volume of heat, from coal, oil, gas, electricity or any other medium for various lengths of time according to the cubical dimensions of the parts being treated, and in the carrying out of this process L0 various temperatures according to the cirboncon- 180 tent of the steel, the range of temperatures being inverse to the variation in carbon. These first steps cause the steel to change into a new structure through a rearrangement 'of the particles iproviding the heat is applied gradually. (/old materials should not be placed directl into a hot furnace. 'When the low critica point of this process determined by previously noted data of a specific carbon is reached the temperature is held uniform for a given time so as to not subject the grains to under stress while the grains are changing positions, etc., thereby effecting a gradual change from Acoarse particles to fine particles evenly distributed.

The temperature is held for but a fraction of the time required to bring the steel up to this point. Then the heating is continued slowly so as to further refine the grain for a time approximating onethird of the initial heating for smaller pieces and one-half for larger sections until the high critical point is reached, approximately twenty to 150 degrees F. higher for the different carbons than the first heat. This difference is a decreasing one as the higher temperatures are reached, being largest for low carbons and practically disappearing when a saturated condition is reached at a theoretical content of about 0.89.

As soon as the required highest temperature is reached an allowance of 25 to 500 F. higher being allowed to compensate for the transfer, the steel is quickly removed from the furnace to a suitable treatment apparatus B, which may consist of a hood which incloses the steel in a hermetically sealed compartment, to which air or other coolini.r agent is supplied in controllable quantity at any desired difference of temperature, and at a pressure which will give a suitabl(I velocity to the cooling agent. This cooling agent may be atmospheric air under pressure, dry steam at about 350 F. or any other gaseous media. Dampers are placed adjacent the steel sections bein treated so as to use local treatment i needed.

In ordinary quenching the hiehest ternperature used is below that found desirable when carrying out this process. Should the highly heated steel be suddenly quenched its quality of structure would be lowered, setting up internal strains, breakages, etc. The particles would become fixed, remaining hard and brittle so as to necessitate further treatment to toughen its structure, such retreatment being however uncertain and not unfrequently hopeless. Such products are a so rce of great danger when used under criltical conditions. The unreliability of quenched steel is aggravated when the sections are of large dimensions because it is impossible to quench such articles without setting up internal stresses due to a shrinking outside encircling an expanding zone which surrounds a contracting center. The various distances from the center being at different temperatures variable `stresses will be set up in objects of circular cross section. `iVlien steel has been mechanically treated under heat it is desirable to allow it to become cold before subjecting it to further heating steps. Whenever' the steel after treatment and physical test shows a very high tensile factor, low elastic limit, elom (ration and reduction of area it may be drawn ack by reheating and tempering to approxi-- mately 600 to 1200O F. according to the carbon content. The lower carbons are submitted to a temperature approximately three-quarters of that to which the higher carbons are subjected and the period over which these temperatures are applied may range from one to two hours. At any event in order to retain as nuich of the fine structure secured b v the first ltreatment as possible steel should not again .be raised above the low critical point. Should one be uncertain after the first heat as to the tensile quality being too high the steel can be cooled as above and similarly retreated.

The approximate variation of temperatures in relation to the carbon content, etc., may be instanced as follows. for 30m G5 carbon over a range of about one hundred and fifty degrees Fahrenheit for the first treat.- ment and for the same carbon constituent over a range of approximately 160 degrees F. for the second treatment. The draw back temperatures used in special eniergencies for the various carbons mentioned ranges about SGOWF. rising with the in crease in carbon while the two heat treat ment temperaturesrise inversely to the increase of carbon. Ordinarily it is found that steels having a carbon content below .40 to A3 require only two consecutive heating stages but those above these percentages may have to be subjected to a draw back because of great brittleness and lack of toughness.

In carrying out the draw back of ma terial having an excessive elastic limit, tensile strengthrand lowelongation and reduction the temperature should be from the lowest point at which steel starts to soften to a degree of temperature below the low critical ort change point and kept at that temperature for a time commensurate'with the results desired. The tem eratures and time allowance though variab e to some degree should be checked at frequent intervals by an ordinary pyrometer or more definite comparable results may be secured through the use of a self recording device.

This process is specially applicable to steels of large section in which the elastic limit, tensile strength, elongation and reduetion of area must be kept hi h. A special t'eature is t'ound in the uni ormity of results produced and the absence of failuresl when products so treated are put to strenuous physical stresses, chemical tests, mieroseopieal deterininations. ete. This results in a superior grade ol output, not attainable hitherto and notably absent in the usual lleat-treatment-qncnching processes.

The ranges of temperature girenare only instanees ot` adaptation and not limitations, the important feature being to hold the temperature uniform over the period'of time when the partieles are rearranging themselves so as not to st ress them and gire a "set to their grouping before the,v are properly retined. 'l`o not use a uniform ap pliration olI heat over this period would seriously modil').r the duality of steel finally protlut-etlY l iluniean tenda-rature l'or eaeh earhon ..utent olA tht` first heating stage is approxi watei the terminal eniyerature ot' the seen.ud heating eorrwpontli f3 to the sante ear .-tiiuptettion. This 'nar be stated in aai. The mean temperature of ne u1-rond treatment approximates the initial temperatures of the tirst heat for eorresptuuling percentages ol earbon, both stages heiner i-onseeutire.

This prowess subita-ts the steel to two ranges ot temperature with a rest period between and very rapid eontrolled cooling. therein' i ing' the best granular rharaev teristies -r e to retain nizwiness without an'ritit-ing 'roughness iur'tility. The various tt-ps ot this process gire flexibility yet eertaimiv of eontrol that hitherto has been unattainable and though lspecially applieable to iarge seetions. such as locomotire axles. ete.. wherein the largest safety factors must he embotlied, the details are amenable to otherpurposes. ln fact any kind of steel article may be suecesst'ully handled in large quantities with uniformity of results.

fliat I claim is:

l. The process ot' heat treating steel which consists first of subjecting the material to a continuous rising heat up to about 13T() degrees F. for 3() point carbon and about 127() degrees F. for 65 point carbon, varying this temperature inversely to the carbon content for intermediate products, arresting the application of heat,

fain another and then subjecting the same to a contin-v uous rising temperature above the upper critical point, and finally applying a` cooling gaseous medium to reduce the temperature rapidly.

2. The process of heat treatment of steels which consists in heating medium steel (of say 6U to 70 point carbon) for the lower critical point, arresting the application of heat, again heating to above the upper critical point, and finally quenching in a gaseous cooling medium.

3. The process ot' heat treating steel after mechanical manipulation which consists in; first, subjeeting the same to a` continuously rising temperature from a cold stato up to about 139() degrees l". for 3U point carbon and about 1240 degrees F. for steels haring approximately twice the carbon content of the former, varying this temperature inversely with the carbon content olE intermediate steels; second, arresting the application of heat to maintain a uniform temperature; third` subjeeting the material to a continuous rising temperature above the upper eritieal point, and fourth, rapidly lowering the temperature of the steel by the eontrolled applieation of a gaseous` medium.

L The protess ot' treating steels alter mechanical .manipulation ahieh eonsists in subjecting a medium steel ranging from about tit) to Tft point rai-lion to two heating stages separated by an arresting period at. about lil-lt) degrees l. i'or .Ult point earbon during which the temperature is held approxin'iately constant. and liually lowering the temperature rapidly by the application of a gaseous medium. the tii'st heating stage being from a eold state to the arresting point and the second from sueh point' to above the upper eritieal point.

The yu'oeess ot treating medium steels ranging approximatelj..v around Jin to ofi point carbon. whit-h consists in gradually raising the temperature trom a old state to about litl and 12TH degrees l". respeetively, holding*r the temperature uniform 'for an appreciable time` again heating to above the upper critical point and linally rapidly reducing the temperature by the application of a gaseous medium without aqueous quenching.

6. The process of heat treatment of steels which consists in slowing and eontii'iuously heating the articles from a eold state after hammering for the lower critical point of the process (of say tl() to T0 point carbon), holding the temperature uniform for a time, further continuously heating the articles to above the upper critical point, rapidly cooling the same in a gaseous medium. and finally in case it is necessary to correct for physical test characteristics to subject tthe material or articles to such draw back temperatures as are needed.

In testimony whereof I atlix my signature in presence of two Witnesses.

DAVID J. SIMPSON.

Witnesses F. W. AMs'rU'rz, A. L. AMs'rU'rz. 

